Electrical power cords are used on almost all electrical devices and appliances. An input or receptacle end of the cord generally plugs into a wall outlet and receives the line power (usually 110-240v AC and 50-60 Hz). An output end of the power cord then connects to the electrical device or appliance desired to be powered.
A large number of electrical devices, including most consumer electronics, require a high-to-low voltage power converter positioned somewhere in the power path between the line power wall outlet and the electrical device itself. This is done for safety and cost reasons, and results in a much safer, lower voltage (typically 5-12 V DC) being delivered to the electrical device under power. As a result, the electrical device/appliance need only meet much less stringent safety approvals.
Unfortunately, the primary side of the power converter in such a configuration is always drawing standby power when plugged into the wall outlet, even if an electrical device/appliance is not plugged into the output end of the power cord which is on the power converter's secondary side. Also, since the high-to-low voltage power converter constantly receives power, whether or not the electrical device is plugged in, the lifetime of the power converter can be significantly shortened.